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Douglas Richie, DPM
Clinical Associate Professor, Department of Biomechanics
at the California School of Podiatric Medicine
Clinical Associate Professor of Podiatric Medicine and Surgery
Western University of Health Sciences
Past President, American Academy of Podiatric Sports Medicine
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Doug Richie: Hello, I'm Dr. Doug Richie. I'm going to present Part 2 of this lecture, focusing on the rule of foot orthoses for the treatment of plantar heel pain. In the previous lecture, we reviewed published research, study and treatment outcomes with various types of foot orthoses to treat plantar heel pain. In the second part of this lecture, we will look at ways we can actually design foot orthoses or prescribe foot orthoses to achieve better outcomes based upon previous published research and understanding of arch mechanisms. In order to understand how to prescribe or design orthoses to treat plantar heel pain, we are going to look at three various areas and come up with sound recommendations. In the previous lecture, we looked at clinical trials that studied pain relief with functional scoring. Now, we are going to look at biomechanical studies of arch mechanisms and we’re going to also look at biomechanical studies which directly measure plantar fascia strain. From this, we're going to try to propose a better understanding of how to prescribe foot orthoses to treat plantar heel pain. When we look at studies of arch mechanisms, we get some interesting insight into how foot orthoses might work and be better prescribed to offload the plantar fascia. The plantar aponeurosis spans the arch of the foot in, as we will show in a few moments, a truss mechanism, which from an engineering standpoint, allows a very simple understanding of the role of tension across the tie rod of the truss known as the plantar aponeurosis. If we look at strain within the plantar fascia, we can learn from recent studies where modeling of the arch mechanism of the foot can let us predict indirectly how strain would develop or be relieved by placing supports under the arch of the foot. These two papers published in 2011 and 2015 looked at semi-custom foot orthoses, not custom orthoses. They provide interesting insight into their role in relieving strain of the plantar fascia. Devices such as these have the ability to relieve strain by over 30%. In this paper, it was interesting that whether it was a prefabricated arch support or heat molded to the individuals in unique shape of their arch, the relief of strain was not enhanced by heat molding. Three different devices were studied that are quite popular and readily available to patients in sporting goods stores, the PowerStep device, the SuperFeet device, and the SOLE support. Here are pictures of these three popular common over-the-counter sports style arch supports or insoles which patients can purchase and place inside of athletic shoes. In this study by Ferber, it was found that the prefabricated orthoses shown in the top two pictures performed better than the prefabricated orthoses in the bottom picture. Ferber attributed this to the fact that the prefabricated orthoses, which had rearfoot posting seem to have a better effect on stabilizing the arch of the foot. When we look at the mechanism of the truss, we understand that there are various components of the truss that can be manipulated with the foot orthoses. The truss mechanism basically says there are two segments, the first ray of the foot, which is the navicular and the media cuneiform and the first metatarsal, and the proximal segment, which is the talus on top of the calcaneus. They are connected by a tie rod, indicated by a T, which is placed under tension. If we want to relieve tension in the tie rod, we can plantarflex the distal strut, which is the first ray, or we can dorsiflex the proximal strut, which is the calcaneus.
Or, we could go to point W on the diagram and simply elevate the junction of the two struts, which is the talonavicular joint. We could also elevate the entire truss off the ground by relieving load and shifting it laterally to the lateral arch of the foot. All of these mechanisms will achieve what we see as we move from the left hand picture to the right hand picture. The tension in the plantar fascia is relieved in the right hand picture. From a mathematical standpoint, it is easy to compute the relationship of the two struts of the truss mechanism, and the angular relationship between those two struts and the tie rod, which is the plantar aponeurosis. It's interesting from a mathematical standpoint using a calculation diagram provided by Darell Philips. That as we raise the calcaneal inclination angle or lower the calcaneal inclination angle, the change in tension of the plantar fascia increases exponentially not in a linear fashion. Changing something as simple as the calcaneal inclination angle or preserving the calcaneal inclination angle in the custom foot orthoses has profound effect on the result in tension of the plantar aponeurosis. We looked at the conformity of a true custom functional foot orthoses manufactured according to the Root principle, and we see how the alignment of the first ray and the inclination angle of the calcaneus can be enhanced and at least preserved by accurate modeling of the plaster cast in the negative impression cast, as well as carrying out the correction of the cast in the laboratory with the construction of the foot orthoses pressed on a positive model. When we design foot orthoses to treat plantar heel pain, we need to look at biomechanical studies which have actually measured how devices will influence strain in the plantar fascia. A very important series of studies was published by Geza Kogler and coworkers from the University of Southern Illinois. These articles were published in 1999 and around that time and have significant influence on the way we understand load in the plantar fascia at least in a static cadaver model. Their first study looked at medial and lateral wedges placed under the foot of cadavers and looked at strain that was either increased or relieved by the placement of wedges in the cadaver models. The first study used nine fresh frozen specimens applied with axial loads simulating static stance. This is important. It's not simulating dynamic gait. Wedges were placed strategically either medial or lateral in the forefoot or the rearfoot, and strain in the plantar fascia was measured before and after application of the wedges. This is a picture of the actual experimental apparatus setup by Kogler with the cadaver specimen mounted on a frame to simulate body weight at static stance. The wedges were either placed medial or lateral in the forefoot or rearfoot, as this picture show in a medial six-degree forefoot wedge compared to a six-degree lateral forefoot wedge placed under the forefoot. In the study, the results were systematic and predictable. Forefoot lateral wedges decreased strain in the plantar fascia each and every time they were placed under the six specimens. Medial forefoot wedges increase strain in the plantar aponeurosis each and every time they were placed in the forefoot. Wedges under the rearfoot had no significant effect. Wedging laterally in the forefoot significantly decrease strain in the plantar aponeurosis.
To understand how a lateral forefoot wedge could decrease strain in the plantar aponeurosis, we can go back and look at our mechanism first described by McConnell, an anatomist from Ireland who published this paper called “The posterior mechanism of the human foot”. In this paper, McConnell introduces the concept of the twisted plate in the lamina pedis of the human foot configuration. This theory was carried forward by McConnell again in 1969, and further by Sarrafian in 1987. This is the actual citation from McConnell’s publication from the proceedings of the Royal Irish Academy published in 1944. The twisted plate mechanism basically describes how the configuration of the bones of the human foot can be moved or twisted in a certain configuration to improve stability and decrease strain on certain structures, particularly on the plantar aponeurosis. In this picture which comes from Sarrafian’s article, the plate is twisted in a configuration where the rearfoot is supinated, designated by S, and the forefoot is pronated. As a result, strain in the planter fascia is relieved as designated by the squiggly line. When the plate is untwisted, the rearfoot is pronated, the forefoot is supinated, and the strain in the planter fascia increases as designated by the straight line in the drawing. Twisting the plate favorably by supinating the rearfoot and pronating the forefoot will raise the longitudinal arch, plantarflex the first ray and decrease strain on the central band of the plantar aponeurosis. This can decompress and improve range of motion of the firsst metatarsophalangeal joint. Here is a picture of a six-degree wedge placed laterally under the left foot in the upper picture and medially under the foot in the lower picture. If we take an x-ray of that same patient without a wedge, we note that this is a rather normal foot structure in a relaxed midstance lateral weightbearing radiograph. With the medial wedge placed under the forefoot as Kogler did in his study, we note that the first ray becomes dorsiflexed. If we measure calcaneal inclination angle in this subject, it's 20 degrees. If we take that same subject and place a lateral forefoot wedge, we note that the calcaneal inclination angle now increases to 25 degrees. Then compared to the previous radiograph, the first ray is now plantarflexed relative to the talus. If we compare a medial wedge to a lateral wedge, we can see how wedging accomplishes an improvement of alignment of the truss mechanism of the arch of the foot and a predictable decreased longitudinal strain of the plantar aponeurosis. Kogler, in his second study published in 1996, measured the effect of foot orthoses on strain of the plantar aponeurosis. He compared five different designs of different types of foot orthoses, both custom and prefabricated in an attempt to understand how orthoses design might offload strain in the plantar fascia. In these studies, three devices significantly reduce strain. One of them was a UCBL custom device, and two of the devices were a softer custom, but a softer more forgiving accommodative type foot bed. Interestingly, the custom rigid Root style custom foot orthoses did not reduce strain in the plantar fascia as did a prefabricated stock orthosis.
Kogler explained the reason why the custom Root style orthosis did not relieve strain in the plantar fascia in the static midstance cadaver model by again looking at the truss mechanism by itself, and speculated that conformity of the medial central portion of the orthosis to the apex of the truss, that would be the talonavicular joint, was not as tight or conforming in the Root style orthosis. Whereas, a UCBL type device number two conformed higher to the medial apex of the truss mechanism. Indeed, a standard Root style foot orthosis has literally minimal contact to the talonavicular joint, but Root himself would have stated that the purpose of his device was not to support the arch, but rather to balance or relieve forces that were compensatory in the human foot due to forefoot to rearfoot deformity or other mechanisms. If we go back and look at the calculations from Daryl Phillips, we can see how a Root style device not supporting the talonavicular joint but supporting the calcaneal inclination angle could significantly reduce strain in the plantar fascia, perhaps, during dynamic propulsive phase of gait. Notwithstanding, in a static cadaver model, Kogler showed that medial posting or medial support under the first ray actually will increase strain in the plantar fascia. A lateral forefoot wedge will predictably decrease strain in the plantar fascia as perhaps by twisting the plate as McConnell had shown, but perhaps by other mechanisms. A lateral forefoot wedge might help plantarflex the first ray, not just by the twisted plate mechanism by simple offloading of the first ray from weight distribution. If we want to reduce strain in the plantar fascia, we can plantarflex the first ray or increase calcaneal pitch. As Kogler showed, we could elevate the talonavicular joint. In a lateral forefoot wedge, we might shift weight laterally to the lateral truss of the foot. All of them could one way or another accomplish the drawing on the right hand side of the screen. If we go back to the traditional custom-molded foot orthosis, how would we accomplish an enhancement of the standard design to make sure that we are adequately offloading the plantar fascia? The first tenet of increasing calcaneal pitch is up to the laboratory that manufactures the foot orthotic. The laboratory should not add any fill or correction to this critical surface of the calcaneus plantarly, and that orthosis should maintain intimate contour to this segment of the foot. In my opinion, the best way to accomplish that is to take a neutral suspension cast and not take a weightbearing cast, because a weightbearing cast will distort that critical part of the anatomy of the human foot necessary to preserve calcaneal pitch. Another orthotic strategy can be accomplished during the neutral suspension cast where the practitioner deliberately pushes down on the first ray to plantarflex the first ray. Then, another strategy in the prescription of the device would be the application of external wedging. Another strategy is a light filler between platforms to preserve a plantarflexed position of the first ray relative to the lesser metatarsals. We will illustrate each of these strategies in the subsequent slides. Pushing down on the first ray while maintaining the neutral suspension casting technique advocated by Root can further enhance orthotic outcome by following the results shown by Kogler and other studies, because in essence, pushing down on the first ray will actually improve alignment of the first ray in the ultimate design of the foot orthotic device. It will also assure that the midtarsal joint is locked and fully pronated.
When one pushes down on the first ray, they should be careful to maintain the subtalar joint in neutral and not further pronate the entire foot but further pronate only the midtarsal joint. By further locking the midtarsal joint, it follows the tenant advocated by Root and many others to improve stability of the human foot, and certainly improve stability correction of the foot orthoses. We can raise the arch of the foot according to the truss mechanism by increasing ground reaction forces under the lateral metatarsals with lateral wedging. We can also increase ground reaction forces under the medial calcaneus. The medial heel skive technique advocated by Kevin Kirby is an excellent way to follow this principle, which actually twist the plate favorably and also improve supination moment around the subtalar joint access which improves stability. The lateral wedge effect advocated by Kogler can also be accomplished by following the Root principle of pronating the midtarsal joint. The idea of the forefoot controlling the rearfoot has been advocated for many years and really did not begin with Root, but it began from Steindler back in 1929, in this important paper discuss a torsion that occurs between the forefoot and the rearfoot, and the influence of the forefoot on the rearfoot. These drawings from Steindler show how pronating the forefoot enhances alignment and stability of the rearfoot. Steindler, in terms of correcting abnormal pronation of the rearfoot talks about how the forefoot and the rearfoot interchange with each other. While the rearfoot pronates, the forefoot compensates by supinating. In order to reverse this mechanism, you should pronate the forefoot on the rearfoot, presumably in a foot orthotic device. Martin Root carried out this principle in his initial lectures and showed that for a foot orthosis to provide stability of the foot, it doesn’t necessarily have to support the medial arch, but instead should be fabricated upon a cast of the foot taken with the midtarsal joint fully pronated. We can appreciate the importance of the neutral suspension cast technique compared to other casting techniques in the following experiment. If we take a patient and cast them as shown in this picture, if the technique advocated by Root where the subtalar joint is positioned neutral and the midtarsal joint is locked and fully pronated, the forefoot to rearfoot relationship which is captured by this cast, and the correction necessary to balance the cast to perpendicular vary significantly if we take that same individual and place their foot on the floor or on foam in a partial weight bearing cast, which would be the second example. Finally, the third example is taking that same individual with their right foot and performing a full weightbearing cast on foam. This is a technique which is popular not just in the podiatric profession but also in chiropractic and other specialties who treat foot and ankle conditions with custom foot orthoses. It's quite interesting to compare what happens in those three situations where the same patient's right foot is casted. In example A on the left hand side of the picture, the Root suspension cast technique captures a forefoot valgus deformity, where the neutral cast to set on the flat surface and the forefeet valgus deformity causes the cast to rock into the direction of inversion. That same patient casted in a partial weightbearing attitude, their right foot in example B converts from a forefoot valgus to what is now a forefoot varus deformity.
This is the same patient. The only difference is how their foot was casted. With a semi-weightbearing cast in B and a full weightbearing cast in C, the previous forefoot valgus in A has now become a forefoot varus. Why is this important? Because when we cast the patient properly with neutral suspension technique and evert the forefoot on to rearfoot to lock the midtarsal joint, in many cases, we will capture a forefoot valgus deformity. If we capture a forefoot varus in a weightbearing cast, the lab will balance the forefoot varus either with an intrinsic post or an extrinsic post, which literally provides a medial wedge effect to the forefoot. This medial wedge effect has already been demonstrated in the previous study by Kogler to increase strain on the plantar aponeurosis. If we capture a forefoot valgus as we did in example A, the lab will post or balance the cast in such a way that the forefoot is supported in a valgus attitude. There will be a lateral wedge effect on the forefoot, which has been demonstrated by Kogler to have a stress relieving effect on the plantar fascia or decreased strain on the plantar fascia. When the lab manufactures and corrects the positive cast, this essential relationship of the first ray relative to the lesser metatarsals must be maintained with minimal fill placed between the balancing platforms. This is an art often lost in today's modern foot orthotic laboratory, which almost mass produced orthoses and fail to preserve the contour of the lesser metatarsals. The correction of intrinsic deformity as we move from a negative impression cast of a right foot to the positive cast in the central picture capturing a forefoot valgus, and then the corrected cast of that same patient where the rearfoot is now in a vertical alignment to the ground. These corrections are accomplished with a balancing platform across the forefoot, but the platform must maintain the relationship of the first ,second, third, fourth and fifth metatarsals. If we plantarflex the first ray in the negative impression cast, the relationship of the first metatarsal to the lesser metatarsals must be preserved in the balancing platforms. The corrected cast must maintain this plantarflexion of the first ray relative to the lesser metatarsals so that the foot orthoses keeps the first ray below the plain on metatarsals two, three, four and five. This little dell or relationship where the first ray is plantarflexed below the second metatarsal may be the essential difference in the success or failure of that foot orthotic specifically treating plantar heel pain. The light filler between the balanced platforms in most cases will preserve the shape of the distal margin of the foot orthoses, where the first metatarsal is plantarflexed in relationship to metatarsals two, three and four. The shape of the metatarsal played itself must preserve the ability of the first ray to plantarflex below the second metatarsal during the propulsive phase of gait, when the hallux dorsiflexes, the windlass is activated and the first ray must freely plantarflex off of the plane of the foot orthotic foot plate. In order to enhance this, practitioners will commonly perform a first metatarsal or first ray cutout to make sure the first ray can plantarflex off of the plate during the propulsive phase of gait. This is not essential in the initial prescription of the foot orthosis, but it might be a modification a practitioner can bring in later if the patient is not responding to the initial treatment with foot orthotic therapy to relieve plantar heel pain. Other enhancements would include the application of a reverse Morton’s extension.
The reverse Morton’s extension is thought to be an enhancement to allow plantarflexion of the first ray below the plane and metatarsals two, three, five. But the reverse Morton’s extension may, in fact, add a valgus wedging effect to the forefoot as described by Kogler, because greater pressure is exerted under the lesser metatarsals, allowing a wedging effect to those metatarsals relative to the first metatarsal. With a reverse Morton’s extension under metatarsals two, three, five, the first ray is allowed to plantarflex as the hallux dorsiflexes during the propulsive phase of gait. Here is the reverse Morton’s extension applied to the extension of a traditional foot orthoses allowing a plane to occur under metatarsals two, three, five, exerting a lateral wedge effect. You can also apply a lateral wedge on the top surface of the orthosis, which further accentuate a wedge effect compared to a simple reverse Morton’s extension. This wedge effect begins at the midshaft of metatarsals two, three, five, and carries out to the edge of the foot plate of the orthosis, or can extend to the sulcus of the foot. The fifth metatarsal receives the highest potion of the wedge and the second metatarsal receives the lowest portion of the wedge. This is basically mimicking the Kogler wedge effect of the foot orthosis to twist the forefoot on the rearfoot. This further locks the midtarsal joint for stability. It is not the same as applying a valgus post to the orthosis. Applying a valgus post externally to the plantar edge of the orthotic simply tilts the entire orthoses in the valgus. It does not wedge the forefoot on the rear foot. It's the wedging of the forefoot on the rearfoot, which must be done to critically offload the plantar fascia. To conclude and review, we've presented clinical studies which often refute or contradict our own clinical experience with foot orthoses. We have to realize that there are problems with these large randomized controlled trials that use average statistics in large groups to come up with trends or recommendations. We've tried to suggest that there are patients within various study groups that do actually respond favorably to custom foot orthotic therapy. In those patients, we need to understand how we can predict favorable outcomes with foot orthotic therapy in specific patients who initially present with plantar heel pain. In looking at research of arch mechanics and strain on plantar fascia, we can come up with the following strategies to enhance traditional approach to custom foot orthotic therapy to relieve plantar heel pain. The first strategy we presented was pushing down on the first ray to maximize eversion of the forefoot and locking of the midtarsal joint during the negative impression casting procedure. We emphasized the value of neutral suspension cast to inverse a semi-weightbearing and full weightbearing casting of the foot. We presented various external wedges or enhancements to the foot orthotic to follow previous research, which shows that lateral wedging of the forefoot on the rearfoot can decrease strain on the plantar fascia. We pointed out areas where the fabrication laboratory can preserve alignment of the metatarsals to assure plantarflexion of the first ray during the propulsive phase of gait. This would include light filler between the platform as well as a cutout of the metatarsal foot plate in some instances to enhance plantarflexion during propulsion. If we do that, we look at what the ideal outcome would be when we treat patients with plantar heel pain. The ideal outcome is not just getting rid of pain, but it’s returning patients to work, and activity, and fitness, and allowing them to function without overbearing footwear restrictions, and restoring strength and flexibility to the foot and to the patient, and most importantly, returning the patient to a pre-injury mobility.
This would be the summation of a positive patient outcome, where patients previously suffering from heel pain can return to fitness, creation and enjoy the benefits of those activities for overall health. Thank you very much.